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Hypersensitivity pneumonitis

What's new

The German Respiratory Society (DGP) and the German Society for Allergology and Clinical Immunology (DGAKI) have released new guidelines for the diagnosis and management of hypersensitivity pneumonitis (HP). Specific IgG testing is recommended when HP is suspected, with the specific IgG determined by the suspected antigen source (e.g., bird keeping, agriculture, mold exposure) or a selection of common antigens (e.g., bird dusts including goose feathers, molds, and thermophilic actinomycetes). Further evaluation for HP is recommended when lymphocyte counts in the bronchoalveolar lavage (BAL) are elevated (≥30%) in patients with interstitial lung disease (ILD). Inhalation provocation testing is suggested only when the diagnosis cannot be confirmed through other methods. Treatment recommendations include avoiding causative agents, corticosteroids for acute or non-fibrotic HP, nintedanib and pirfenidone for chronic fibrotic progressive HP, and early evaluation for lung transplantation. .

Guidelines

Key sources

The following summarized guidelines for the evaluation and management of hypersensitivity pneumonitis are prepared by our editorial team based on guidelines from the German Society for Pneumology and Respiratory Medicine (DGP/DGAKI 2025), the American College of Chest Physicians (ACCP 2021), the Latin American Thoracic Association (ALAT/JRS/ATS 2020), the American Thoracic Society (ATS 2011), and the British Thoracic Society (BTS/TSANZ/ITS 2008).
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Screening and diagnosis

Diagnosis: as per ACCP 2021 guidelines, consider using clinical improvement with antigen avoidance, if an inciting antigen is identified and then completely avoided, to support the diagnosis in patients with suspected HP. Avoid relying solely on the lack of clinical improvement with antigen avoidance to rule out the diagnosis of HP.
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Classification and risk stratification

Classification
As per DGAKI/DGP 2025 guidelines:
Classify HP as either acute or chronic, with particular attention to occupational medicine considerations.
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Classify chronic HP further into fibrotic or non-fibrotic phenotypes to reflect the implications of fibrosis on prognosis and treatment.
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Diagnostic investigations

General principles
As per ACCP 2021 guidelines:
Consider using a multidisciplinary discussion for diagnostic decision-making in patients with suspected HP.
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Consider including an occupational medicine specialist and an environmental hygienist in the multidisciplinary diagnostic workup in patients with suspected HP, if the inciting antigen is thought to be related to an occupational exposure especially if the source of exposure is obscure or unverified.
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More topics in this section

  • Exposure history

  • Antigen-specific antibodies

  • Antigen-specific lymphocyte proliferation testing

  • Provocation testing

  • CT

Diagnostic procedures

Bronchoalveolar lavage
As per DGAKI/DGP 2025 guidelines:
Perform bronchoalveolar lavage with differential cell counts in patients with newly diagnosed ILD suspected of having HP.
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Obtain further diagnostic evaluation for HP in case of elevated lymphocyte counts (≥ 30%) in bronchoalveolar lavage in patients with ILD. Do not use CD4/CD8 ratios in bronchoalveolar lavage analysis to diagnose HP.
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  • Lung biopsy

Medical management

Avoidance of causative antigens: as per DGAKI/DGP 2025 guidelines, obtain antigen avoidance testing for diagnosis in patients with clinical symptoms indicative of acute HP and an obvious antigen source or antigen, if the antigen source has not been confirmed in other diagnostic steps.
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  • Corticosteroids

  • Antifibrotic agents

Surgical interventions

Lung transplantation: as per DGAKI/DGP 2025 guidelines, evaluate patients with chronic fibrotic HP of a progressive phenotype for lung transplantation at an early stage, as necessary.
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Specific circumstances

Patients with HP related to Aspergillus
As per ATS 2011 guidelines:
Advise avoidance of Aspergillus exposure in patients with HP related to Aspergillus and, when necessary, initiate corticosteroid therapy up to 60 mg/day, tapering over 1 month.
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Do not use antifungal therapy in patients with HP related to Aspergillus.
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